JPH0335025A - Substrate for print circuit board having low dielectric constant - Google Patents

Abstract

PURPOSE:To obtain the title substrate capable of stably preparing a substrate for light-weight printed circuit board having low dielectric constant by constructing the substrate with a cloth composed of a conjugate fiber consisting of a liquid crystal polyester based resin, etc., and inorganic fiber. CONSTITUTION:The aimed substrate using a cloth composed of (A) a composite fiber consisting of (i) a liquid crystal based resin having >=30000 number-average molecular weight and capable of forming the surface and (ii) another polymer containing fluorine, having lower dielectric constant than that of liquid crystal, free from endothermic peak based on melting of the component i when measured by raising up to 400 deg.C using differential.scanning.calorie meter sealed with nitrogen and (B) inorganic fiber (e.g. glass fiber).

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a substrate for a printed circuit board having a low dielectric constant and a method for producing the same. More specifically, the present invention relates to a low dielectric constant printed circuit board base material that is lightweight and has stable physical properties and is made of inorganic fibers and organic high-strength composite fibers, and a method for manufacturing the same.

[Conventional technology]

Printed circuit boards made of resin fabrics containing fluorine impregnated with epoxy resin are widely used.

However, such printed circuit boards have the following problems. That is, (2) the dielectric constant of the printed circuit board is high because the resin containing fluorine has a high dielectric constant.

■It's heavy.

For this reason, its uses have been limited.

Several techniques have been disclosed to solve these problems. A typical example is the use of a resin containing fluorine and having a low dielectric constant.

The base fabric is quartz fiber. In the case of quartz fibers, it is certainly possible to lower the dielectric constant.

However, it is not a solution to the 2M problem. Another problem is that it is very expensive.

Further, Japanese Patent Application Laid-open No. 154690/1983 discloses a technique using micro hollow bodies.

However, since the distribution of micro hollow bodies is often non-uniform in this method, there is a drawback that the physical properties are not uniform. In addition, the micro hollow bodies became stress concentration points, often resulting in a decrease in the strength of the printed circuit board.

Further, an attempt to reduce the weight by using organic aramid fibers is disclosed in Japanese Patent Application Laid-Open No. 11289/1989. but,
Such aramid fibers have the drawbacks of high water absorption and unstable physical properties.

That is, there has been no technology that simultaneously achieves a lower dielectric constant, lighter weight, and stable physical properties.

[Problem to be solved by the invention]

That is, one object of the present invention is to provide a base material for a printed circuit board that has a low dielectric constant, is lightweight, and has high dimensional stability, and a method for manufacturing the same.

[Means to solve the problem]

In view of the current situation, the inventors of the present invention have arrived at the present invention as a result of extensive studies without being bound by conventional research concepts. In order to solve the above problems, the present invention has the following configuration.

(1) A base material for a low dielectric constant printed circuit board made of a fabric made of composite fibers (A) made of a liquid crystal polyester resin and other resins and inorganic fibers (B).

(2) The base material for a low dielectric constant printed circuit board according to item 1, wherein the liquid crystalline polyester resin forms the surface of the composite fiber (A).

(3) The number average molecular weight of the liquid crystal polyester resin.

2. The substrate for a low dielectric constant printed circuit board according to 1 or 2, which has a dielectric constant of 30,000 or more.

(4) Liquid crystal polyester resin is rated at 400% by nitrogen-sealed differential scanning calorimeter.
4. The substrate for a low dielectric constant printed circuit board according to any one of 1 to 3, which is a composite fiber (A) that does not have an endothermic peak due to melting of the component when measured up to .degree.

(5) The base material for a low dielectric constant printed circuit board according to item 1, wherein the other resin is a composite fiber having a dielectric constant of zero than that of the liquid crystalline polyester resin.

Honsuhari (6) The other resin is a resin containing fluorine 1==t≠
Base material for low dielectric constant printed circuit boards described in Wagasa.

(7) The inorganic fiber (B) is a resin containing fluorine.
A base material for a low dielectric constant printed circuit board as described in .

(7) The base material for a low dielectric constant printed circuit board as described in 1C≠*Hanbonka, in which the inorganic fibers (A) and the inorganic fibers (B) are mixed yarns.

(9) The base material for a low dielectric constant printed circuit board according to item 1, wherein the composite fiber (A) and the inorganic fiber (B) are mixed yarns.

QO) The base material for a low dielectric constant printed circuit board according to 1, wherein both the composite fiber (A) and the inorganic fiber (B) are continuous fibers.

(11> The base material for a low dielectric constant printed circuit board according to 1, wherein the fabric is a woven fabric.

(12) A first step of melt-composite spinning the resin according to claim 1, wherein the fabric is a woven fabric, such that the liquid crystal polyester resin forms at least the surface of the composite fiber.

After mixing the composite fiber with inorganic fiber to form a mixed fiber yarn.

A low dielectric constant printed circuit board characterized by comprising a second step of weaving or interweaving without forming a mixed fiber yarn, and a third step of heat-treating the liquid crystal polyester resin at a temperature of (melting point -100)°C or higher. The second step for the base material may be carried out after any step after the first step).

(13) The other resin is a thermoplastic fluorine-containing resin 1
2. The method for producing a base material for a low dielectric constant printed circuit board according to 2.

(14) The method for producing a substrate for a low dielectric constant printed circuit board according to 12, wherein the heat treatment is performed until the liquid crystal polyester resin has a number average molecular weight of 30,000 or more.

The present invention will be explained in more detail below.

According to the present invention, it is possible to easily achieve low dielectric constant, lightweight,
Moreover, it is truly surprising that a substrate for printed circuit boards with stable physical properties can be produced at low cost.

The base material for a printed circuit board of the present invention has only inorganic fibers and liquid crystal polyester composite fibers as essential materials, and both constitute a fabric form.

As inorganic fibers, various fluorine-containing resins such as so-called E-glass fibers, quartz fibers, and alumina fibers can be widely used. Among these inorganic fibers, particularly preferred are FF, E glass fiber, and D glass fiber.

The cross-sectional shapes of such fibers include ○-shaped cross-sections, cross-shaped cross-sections, and ∆-shaped cross-sections.
Shapes, ellipses, etc. can also be used, and are not particularly limited. Also particularly preferred are irregular cross-section fibers such as those disclosed in JP-A-61-244088. Furthermore, the fineness is not particularly limited either. In particular, fibers having a thickness of 1 μm to 20 μm are particularly preferably used.

Next, composite fibers will be explained.

The composite fiber of the present invention is a fiber made of a liquid crystal polyester resin and another resin.

The liquid crystal polyester resin is composed of a thermoplastic liquid crystal forming polyester or polyester amide having a mesogen group in its main chain. Although such resins inherently exhibit thermoplasticity, the fibers of the substrate for printed circuit boards of the present invention do not need to be thermoplastic; rather, in cases where heat resistance is particularly required. ! Preferably, it is not plastic.

There are various main chain type liquid crystalline polyester resins, and there are no particular limitations, and conventionally known resins can be widely used.

There are various types of aromatic polyesters, and conventionally known ones can be used without any particular limitation.

Particularly preferred is a composite fiber using a liquid crystal polyester resin having the following structural units.

That is, here.

X is hydrogen.

halogen.

carbon number 4 or less Represents an alkyl group.

Here, Σnt=100 in each structural formula. Particularly preferred is a point in which each structural formula has an ni force of 4 or more. Moreover, various substituents including halogen etc. may be added to each formula.

These materials are particularly preferred because they have high melt formability, high strength, and also have a good melting point and glass transition point.

In addition, the dielectric constant is low, and the thermal shrinkage is also low.
Moreover, it is preferable because it has a low water absorption rate.

Next, conventionally known liquid R polyester resins made of aromatic polyester amide can be widely used, and are not particularly limited.

Especially in the case of fibers made of liquid crystal polyesteramide,
There is a benefit that can be easily made infusible by high temperature treatment. Therefore, it is particularly effective for places that require heat resistance. The conjugate fiber of the present invention essentially contains such a clear-crystalline polyester resin.

Another essential component is the power of other resins.

Other resins include conventionally known thermoplastic resins. There is no particular limitation as long as it can be spun simultaneously with the liquid crystal polyester component.

Various thermoplastic fluororesins, nylon resins, polyesters made of polyethylene terephthalate, polyphenylene sulfide, and polyesters.

- Highly functional resins such as tilketone can be widely used, and among such resins, those having a lower dielectric constant than liquid crystal polyester resins are particularly preferred.

That is, what is particularly preferable?

copolymer of tetrafluoroethylene and ethylene (ETFE), polyfluoroalkoxyethylene and copolymer of tetrafluoroethylene (PFA), copolymer of tetrafluoroethylene and hexafluoropropylene (FEP), Copolymer of tetrafluoroethylene, hexafluoropropylene, and polyfluoroalkoxyethylene (EP
E), and.

Examples include thermoplastic fluororesins partially containing chlorine, and thermoplastic fluororesins such as tetrafluoroethylene to which a plasticizer is added.

Next, the composite form of the composite fiber is not particularly limited, and conventionally known forms can be widely used.

That is, the relationship of the resin according to claim 1, in which the fabric is a woven fabric, can be any of a core-sheath type, a polymer blend fiber, a bimetal type, a so-called polymer array type, a two-part peel type, a split peel type with a hollow space, etc. It can be used. Further, any combination of the resins according to claim 1, wherein the fabric is a woven fabric, may be used.

However, in such a structure, especially in the case of a composite fiber of liquid crystal polyester resin and fluororesin, if the binder of the printed circuit board is a resin that does not contain fluorine, the fluororesin will not appear on the surface layer of the composite fiber. It is preferable. That is, it is preferable that the surface of the composite fiber is made of liquid crystal polyester resin. Since the fluororesin has poor adhesiveness with other resins, it is preferable that the fluororesin exists inside the composite fiber. That is, in the case of a core-sheath type fiber, the fluororesin is preferably a core component. In addition, if it is a polymer array type fiber,
The fluororesin is preferably an island component. This allows good adhesion to the binder of the printed circuit board. In addition, if the liquid crystal polyester component has low adhesion to the binder of the printed circuit board, a highly adhesive resin may be placed further outside the liquid crystal polyester component.
Also preferred are conjugate fibers. In addition, a fluorine-based binder is used as the binder for the printed circuit board.

This is not the only case where the binder such as fluororesin constituting the fibers adheres well, and various composite forms can be widely used.

The thickness, cross-sectional shape, etc. of the composite fiber of the present invention are not particularly limited, and can be widely used.

Regarding the cross-sectional shape, ○, △9, oval, etc. can be used. In addition, the hollow cross section, and the shape that is part of the hollow fiber,
A cross-sectional shape of a lotus root is also preferable. In particular, hollow fibers and their deformed fibers are preferred because they have the effect of reducing the dielectric constant. Note that these hollow fibers may be continuous hollow fibers, but more preferably they are partially filled fibers.

When such fibers are used for printed circuit boards, insulation defects due to copper migration are unlikely to occur.

It is also preferable that the fibers have fine pores inside or on their surfaces. Microporosity is also effective in reducing the dielectric constant.

These fibers do not need to all have the same shape in the length direction, and the shapes of the fibers that make up the thread do not need to all have the same shape, but threads can be made from fibers with various minx cross-sectional shapes. may be configured.

Next, regarding the fineness of the composite fibers, if the m-fibers are too thick, the base material for the printed circuit board becomes thick and it is not possible to form a compact printed circuit board, which is not preferable.

Therefore, it is preferably 6 N or less.

It is more preferable that the fiber is 5 denier or less, and even more preferable that the fiber is 2 denier or less. Also, printed circuit boards made of high-denier fibers have a smooth surface.
Furthermore, the flexibility is also poor, which is not desirable, ie, printed circuit boards made of thin fibers are better.

Next, the number average molecular weight of the liquid crystal polyester component is preferably 30,000 or more. More preferably, it is 50,000 or more. Such a high molecular weight liquid crystalline polyester composite fiber is preferable because it not only has a high two strength and one modulus of elasticity, but also has high fatigue resistance. In particular, such fibers are preferred because of their high buckling strength and have high strength and high elastic modulus.

In addition, when the liquid crystalline polyester composite fiber is sealed with nitrogen and measured up to 400°C with a differential scanning calorimeter (hereinafter abbreviated as DSC), fibers that do not have an endothermic peak due to melting of the liquid crystalline polyester component are preferable. A base material for a yellowtail or aluminum substrate made of such fibers has high heat resistance.

The substrate for a printed circuit board of the present invention is made of such inorganic fibers and liquid crystalline polyester composite fibers, and is in the form of a cloth. Fabric is a woven or knitted fabric.

It refers to nonwoven fabrics, composites of woven or knitted fabrics and nonwoven fabrics, and products in which films or the like are laminated thereon. Among such fabrics, particularly preferred fabrics are woven fabrics. Woven fabrics are preferable because they have high dimensional stability in warp and weft.

It also has the advantage of being thin. Textiles are generally warp,
In addition to the weft yarns, multi-axial fabrics in which yarns are inserted diagonally to the warp, such as at 45° C., are also preferred in order to increase dimensional stability in all directions. Furthermore, a laminate of a woven fabric and a nonwoven fabric is also preferable for the same reason.

The fabric may be composed of continuous long fibers. Further, it may be composed of short fibers. Further, it may be composed of a mixed fiber of long fibers and short fibers. However, it is particularly preferable that both the fi fiber and the composite fiber are composed of continuous fibers. Continuous fibers have the great advantage of increased dimensional stability.

Next, the morphology of the fibers in a fabric made of such inorganic fibers and composite fibers will be described.

When looking at the morphology of the fibers from the distribution state in the fabric of both fibers constituting the fabric, there are basically the following four types.

■Inorganic fibers and composite fibers are basically a mixture of single fibers, and the fibers directly make up the fabric.

Typical examples include paper-like fabrics and nonwoven fabrics in which inorganic fibers and composite fibers are mixed at the fiber level.

■Inorganic fibers and composite fibers are mixed to form yarn.

The threads constitute the fabric.

A typical example of this is a fabric made of yarn in which composite fibers and inorganic fibers are mixed at the fiber level. That is, examples thereof include yarns in which composite fibers and inorganic fibers are mixed (mixed fiber yarns), and fabrics made of yarns in which composite fibers and inorganic fibers are mixed (mixed yarns).

■Inorganic fibers and composite fibers each make up threads, and these threads make up fabric.

Typical examples include fabrics made of composite fibers and inorganic fibers interwoven or knitted together.

A combination of ■■ to ■.

In case (2), the fabric has the advantage that the zero dimension stability is uniform because the inorganic fibers and composite fibers are uniformly distributed in all parts of the fabric.

In the case of (2), the mixed fiber yarn makes the yarn, and the yarn makes the fabric, and when the fabric is a woven fabric, it is particularly preferable because it has high 9-dimensional stability.

The case of (2) is the same as the case of (2), and when the fabric is a woven fabric, it becomes a fabric with high strength and high dimensional stability as in (2).

Examples of ■ are ■ and ■, ■ and ■, and ■ and ■.
There are also combinations of ■, ■, and ■.

In any case, it is preferable that (1) to (2) be appropriately selected depending on the purpose and use.

There is no problem even if the composite fibers and inorganic fibers constituting such a fabric are partially fused. In addition, liquid crystal polyester composite fibers may be fused to each other.
A mixed fiber yarn further improves the dimensional stability of the printed circuit board. Furthermore, since the substrate for printed circuit boards is not easily deformed when impregnated with various resins when manufacturing printed circuit boards, the yield of printed circuit board production may be improved.

Next, the ratio of inorganic fibers to composite fibers varies greatly depending on the purpose and use; however, it is generally preferable to have a larger amount of composite fibers when lighter weight and lower dielectric constant are required.

Especially when heat resistance is required, it is preferable to have a large amount of inorganic fiber.

The ratio of composite fibers and inorganic fibers should be determined by clarifying the intended use. Basically, it is preferable that the amount of composite fibers is larger, and it is preferable that the content is 15 to 90 M1%. More preferably, it is 30 to 90% by weight.

The thickness of the printed circuit board base material of the present invention is not particularly limited. You can make everything from extremely thin to thick items.

In particular, if thin fibers are used for both composite fibers and fluorine-containing resin, the fabric will be thin. The thickness of conventional fabrics made only of fluorine-containing resins could not be controlled by heat pressing, but the thickness of the fabric of the present invention can be controlled by applying appropriate temperature and pressure.

Next, the manufacturing method of the present invention will be described.

First, the resin according to claim 1, wherein the fabric is a woven fabric, is subjected to melt composite spinning. Here, the composite spinning in the present invention refers to a spinning method in which two or more types of polymers are simultaneously discharged from the same hole of a spinneret. That is, the so-called core-sheath type, bimetal type,
Polymer array type with a large number of cores, blend spinning method, so-called 9-part peel type, micro-split type with a large number of 2-piece peels, hollow polymer array type, hollow split peel type, etc. is cited as a representative example.

Fibers such as triple core-sheath fibers are also preferred.

Other resins used in composite spinning are not particularly limited as long as they can be spun simultaneously with the liquid crystal polyester resin. And what is more preferable is a material with a dielectric constant lower than that of liquid crystal polyester resin.

It is a resin that has higher adhesiveness with the binder of printed circuit boards.

Furthermore, the liquid crystal polyester resin is continuous within the composite fiber.

Particularly preferred spinning methods are the core-sheath method and the polymer array method. For some reason, spinning using this particularly preferred method improves the strength of the conjugate fiber, and also makes it easier to produce the fiber.

As described above, when the spinning method according to the present invention is used, the following major advantages can be obtained, although the reasons thereof are unclear.

(i) From the method point of view, (a) if such a configuration is adopted, for some reason, the spinning becomes stable and can be spun at a higher speed than when spinning liquid crystal resin alone. Therefore, productivity is improved.

■From things (B) Thin liquid crystalline polyester fibers are produced.

(b) Many liquid crystalline polyester fibers can be made in other resins.

(d) Fibers with higher strength and higher elastic modulus can be obtained than those obtained when the liquid crystalline polyester resin is spun alone.

When performing such composite spinning, it is preferable that the spinning speed be high. A high spinning speed facilitates the orientation of the liquid crystalline polyester resin component, which is preferable. What is the spinning speed?

The speed is preferably 500 m/min or more, more preferably 1000 m/min or more, and still more preferably 2000 m/min or more. In this way, the liquid crystal polyester resin is oriented and becomes a high-strength fiber. In the fiber spinning process, there is no problem in applying a magnetic field, an electric field, microwaves, plasma treatment, heating below the first spindle, or creating a vacuum below the second spindle as appropriate.

The ratio of the resin according to claim 1, in which the fabric in this step is a woven fabric, is not particularly limited. In some cases, even if the liquid crystal polyester component is 97% by weight, spinning is possible. The ratio may be selected depending on the purpose.

Next, the composite fibers obtained in this way are interwoven with inorganic fibers, and m
or as yarn mixed with inorganic fibers. The method for preparing the mixed yarn is not particularly limited, and conventionally known methods such as twisting, twisting, false twisting, and fluid treatment can be used.

In this way, fibers made into a mixed yarn, yarns made only of composite fibers, or yarns made of inorganic fibers are woven.

In the case of mixed fiber yarn, it may be woven alone or mixed with composite fibers or inorganic fibers. In addition.

When composite fibers constitute threads by themselves, they are interwoven with inorganic fibers. Although there are various types of mixed weave structures, it is preferable to use both composite fibers and inorganic fibers for both the warp and weft. The same applies to multi-axis textiles, and it is preferable to use both yarns for each axis. The weaving machine can be a conventional Wi machine for fluorine-containing resin or carbon fiber without any particular problem. The texture is also not particularly limited.

The fabric thus obtained is heat-treated at a temperature higher than (melting point -100)'C of the liquid crystal polyester resin. The heat treatment is performed in air, under a stream of inert gas such as nitrogen, or under vacuum.

When the other resin has heat resistance and chemical resistance and the surface of the composite fiber is mainly composed of these resins, the treatment may be carried out in air.

However, in other cases, it is preferable to carry out in air, under a flow of inert gas such as nitrogen, or under vacuum.

Particularly preferably, the liquid crystal polyester resin has a melting point of −5
0) Processing at a high temperature of 'C or higher.

Since the melting point of the liquid crystal polyester component increases by heat treatment, it is also preferable to carry out the heat treatment at a temperature equal to or higher than the original melting point of the liquid crystal polyester component.

By doing so, the melting point and molecular weight of the liquid crystal polyester resin are increased, and the heat resistance is improved. At the same time, the strength also increases.

It is preferable to carry out the heat treatment until the number average molecular weight becomes 30,000 or more, particularly preferably 50,000 or more. Note that this value varies greatly depending on the type of resin and its shape B (fineness, cross-sectional shape, etc.), so it is important to appropriately adjust the heat treatment time and temperature according to the resin.

Further, if the heat treatment is further strengthened, the liquid crystal polyester component becomes infusible, and an endothermic peak due to melting may not appear even when measured by DSC.

This increases the strength and heat resistance of the liquid crystal polyester component.

Further, if necessary, it is also possible to fuse the composite fiber and the inorganic fiber. Conventional fibers made of thermoplastic resins such as nylon shrink significantly when melted, but the composite fiber of the present invention shrinks extremely little when melted, so it can be used as an inorganic fiber without deforming the fabric structure. This makes it possible to fuse the two. This tendency is particularly high for liquid crystalline polyester composite fibers having a number average molecular weight of 30,000 or more.

Also, i! ! By carrying out heat pressing or the like when appropriate, a thin, high-strength, and good printed circuit board base material can be produced.

The base material for printed circuit boards of the present invention is firstly impregnated with resin,
After wiring processing, it becomes a printed circuit board. In this process, there is no problem in performing a treatment for removing a sizing agent from the resin containing fluorine, a silane treatment, a plasma treatment, etc.

The printed circuit board obtained by this method is lightweight, has a low dielectric constant, and has dimensional stability equal to or higher than that of conventional circuit boards. In addition, if the inorganic fibers are selected appropriately, a printed circuit board having the above-mentioned characteristics can be obtained at low cost. Therefore, the base material for printed circuit boards according to the present invention can be effectively used not only for high-speed calculation printed circuit boards and high-frequency printed circuit boards, but also for high-speed calculation of conventional printed circuit boards.

The present invention will be explained in more detail with reference to Examples below.

It goes without saying that the present invention is not limited to these embodiments.

〔Example〕

Example 1 As shown below, a sample consisting of liquid crystalline polyester fibers and inorganic fibers was woven to produce a base material for a printed circuit board. There were no particular problems in each process.

A. Silk spinning conditions ■ Sheath component (resin for liquid crystal polyester fiber): Liquid crystal resin Vectra As2 manufactured by Hoechst Celanese Co., Ltd. in the United States
O ■ Core component (other resin): ETF manufactured by Daikin Industries ■ Core/Sheath = 55/45 (weight ratio) ■ Spinning temperature = 315°C ■ Spinning speed = 500 m/min ■ Stretching ratio = None.

B. Characteristics of the obtained fiber ■ Fineness and number of filaments of liquid crystal resin composite = 600 denier (hereinafter referred to as d), 200 (single fiber d = 3 d) ■ Strength = 6 g/d ■ Idenier -1 , 9% B, for use in printed circuit boards Next, this fiber and the so-called E glass fiber were woven into a yarn having a single fiber thickness of 15 μm and a filament count of 200, alternating both warp and weft yarns. The number of stitches is 40 warp threads/
25 tm, and the number of wefts was 33/25n.

Next, the fabric was wrapped around a stainless steel cylinder with many holes, and the temperature was raised to 255° C. over 3 hours while nitrogen was flowing through the core, and the fabric was left at this temperature for 2 hours to perform high-temperature heat treatment.

Next, the fabric was taken out, passed through a heating furnace heated to 340°C, and then pressed with a hot press roller at 280°C to fuse the composite fibers and the inorganic fibers.

The strength of the composite fiber is 11 g/d, the elastic modulus is 220 g/d, and the number average molecular weight of the liquid crystal polyester component is approximately 60,000, and no peak due to melting of the liquid crystal polyester resin is observed under DSC at less than 400°C. Subsequently, a printed circuit board was prepared by impregnating it with a resin in the same manner as described in JP-A-61-183992.

The dielectric constant was 3.6. All of the comparative examples were approximately 10% lighter than the printed circuit boards made of glass fiber used in this example. Further, the dielectric constant was 4.2, which was higher than in the actual test. There was no difference in one-dimensional stability between the two.

In other words, a lightweight printed circuit board with a low dielectric constant was made.

Example 2 The composite fiber of Example 1 and the glass fiber of Example 1 were combined into two
00 pieces, and 100 pieces of the latter.

The yarn was processed into a ts yarn at 80 times/m to form a mixed fiber yarn. Thereafter, it was processed in the same manner as in Example 1 to obtain a base material for a printed circuit board, and further impregnated with a resin to obtain a printed circuit board. The dielectric constant was 3.4. It was also about 15% lighter than a printed circuit board made of glass fiber in the same manner. In addition, the dielectric constant was 4.3, which was higher than the actual value. There was no difference in one-dimensional stability between the two.

In other words, a lightweight printed circuit board with a low dielectric constant was made.

〔Effect of the invention〕

The following effects can be obtained by the present invention.

■Low dielectric constant and lightweight base materials for printed circuit boards can be stably produced.

■In particular, composite fibers that use fluororesin for the core (island) component and liquid crystalline polyester resin for the sheath (sea) component will have good adhesion with the binder for printed circuit boards and have an extremely low dielectric constant. You can make printed circuit boards.

■In particular, liquid crystalline polyester resin is used for the core (island) component,
If the sheath (sea) component is made of a composite fiber that uses a resin with higher adhesiveness than the liquid crystal polyester system.

Adhesion with the binder for printed circuit boards is improved, and printed circuit boards with a low dielectric constant can be stably produced.

Claims (14)

[Claims] (1) A base material for a low dielectric constant printed circuit board made of a fabric made of composite fibers (A) made of a liquid crystal polyester resin and other resins and inorganic fibers (B). (2) The substrate for a low dielectric constant printed circuit board according to claim 1, wherein the liquid crystal polyester resin forms the surface of the composite fiber (A). (3) The substrate for a low dielectric constant printed circuit board according to claim 1 or 2, wherein the liquid crystal polyester resin has a number average molecular weight of 30,000 or more. (4) Liquid crystal polyester resin is rated at 400% by nitrogen-sealed differential scanning calorimeter.
The substrate for a low dielectric constant printed circuit board according to any one of claims 1 to 3, which is a composite fiber (A) that has no endothermic peak due to melting of the component when measured up to a temperature of .degree. (5) The base material for a low dielectric constant printed circuit board according to claim 1, wherein the other resin is a composite fiber having a dielectric constant lower than that of the liquid crystal polyester resin. (6) The substrate for a low dielectric constant printed circuit board according to claim 1 or 5, wherein the other resin is a resin containing fluorine. (7) The base material for a low dielectric constant printed circuit board according to claim 1, wherein the inorganic fiber (B) is a glass fiber. (8) The substrate for a low dielectric constant printed circuit board according to claim 1, wherein the composite fiber (A) and the inorganic fiber (B) are mixed yarns. (9) The base material for a low dielectric constant printed circuit board according to claim 1, wherein the composite fiber (A) and the inorganic fiber (B) are fused together. (10) The substrate for a low dielectric constant printed circuit board according to claim 1, wherein both the composite fiber (A) and the inorganic fiber (B) are continuous fibers. (11) The base material for a low dielectric constant printed circuit board according to claim 1, wherein the fabric is a woven fabric. (12) A first step of melt-spinning liquid crystal polyester resin and other resins so that the liquid crystal polyester resin forms at least the surface of the composite fiber, and the composite fiber is mixed with inorganic fiber to form a mixed fiber yarn. After that, a second step of weaving or interweaving without making it into a mixed fiber yarn, and a third step of heat-treating the liquid crystal polyester resin at a temperature of (melting point -100) degrees Celsius or higher. A method for manufacturing a base material for a printed circuit board (the third step may be performed after any step after the first step). (13) The method for producing a substrate for a low dielectric constant printed circuit board according to claim 12, wherein the other resin is a thermoplastic fluorine-containing resin. (14) The method for producing a substrate for a low dielectric constant printed circuit board according to claim 12, wherein the heat treatment is performed until the number average molecular weight of the liquid crystal polyester resin reaches 30,000 or more.